Wrong use of classmethod decorator

[cayetanobv]

There is a generalized wrong use of classmethod decorator in plugin. In a lot of cases classmethod decorator must be changed by staticmethod decorator. In other cases methods are simply instance methods (no decorator is needed at all).

I've counted 68 use cases to review.

Related docs:

• https://docs.python.org/3.6/library/functions.html?highlight=classmethod#classmethod
• https://stackoverflow.com/questions/12179271/meaning-of-classmethod-and-staticmethod-for-beginner

[cvvergara]

@cayetanobv This needs review before making the final tag

[cayetanobv]

We can live with this issue for now. I can't do this week or the next. I think we can release final version without this.

[cvvergara]

changing milestone then

[cayetanobv]

Removed milestone for this issue. When we release version we add to new milestone created.

[cvvergara]

Moved to a next milestone